Telecommunications networks transport signals between user equipment at diverse locations. A telecommunications network includes a number of components. For example, a telecommunications network typically includes a number of switching elements that provide selective routing of signals between network elements. Additionally, telecommunications networks include communication media, e.g., twisted pair, fiber optic cable, coaxial cable or the like that transport the signals between switches. Further, some telecommunications networks include access networks.
For purposes of this specification, the term access network means a portion of a telecommunication network, e.g., the public switched telephone network (PSTN), that allows subscriber equipment or devices to connect to a core network. For example, an access network is the cable plant and equipment normally located in a central office or outside plant cabinets that directly provides service interface to subscribers in a service area. The access network provides the interface between the subscriber service end points and the communication network that provides the given service. An access network typically includes a number of network elements. A network element is a facility or the equipment in the access network that provides the service interfaces for the provisioned telecommunication services. A network element may be a stand-alone device or may be distributed among a number of devices.
There are a number of conventional forms for access networks. For example, the digital loop carrier is an early form of access network. The conventional digital loop carrier transported signals to and from subscriber equipment using two network elements. At the core network side, a central office terminal is provided. The central office terminal is connected to the remote terminal over a high-speed digital link, e.g., a number of T1 lines or other appropriate high-speed digital transport medium. The remote terminal of the digital loop carrier typically connects to the subscriber over a conventional twisted pair drop.
The remote terminal of a digital loop carrier is often deployed deep in the customer service area. The remote terminal typically has line cards and other electronic circuits that need power to operate properly. In some applications, the remote terminal is powered locally. In some networks, the remote terminal is fed power over a line from the central office. This is referred to as line feeding or line powering and can be accomplished through use of an AC or a DC source. Thus, if local power fails, the remote terminal still functions because it is typically powered over the line using a battery-backed power source. This allows the remote terminal to offer critical functions like lifeline plain old-fashioned telephone service (POTS) even during a power outage.
Over time, the variety of services offered over telecommunications networks has changed. Originally, the telecommunications networks were designed to carry narrowband, voice traffic. More recently, the networks have been modified to offer broadband services. These broadband services include services such as digital subscriber line (DSL) services. As time goes on, other broadband services will also be supported. These new services often come with increased power requirements.
Line-powered network elements in access networks rely on the central office for continuous power. As the distance between the central office and a network element increases, the amount of power required to provide a constant voltage at the network element increases. In some instances a faulty channel card, a short on a channel card or even improper installation of a channel card causes an increase in the current draw at the line powered network element. The current increases and the voltage received at the line powered network element (CPE, RT) decreases. When the input voltage at the network element begins to fall an indicator is needed to prohibit a power source shut down.
Input voltage may be too low, and current draw may be too high for many reasons. If the span used for powering the network elements is too high in resistance, the voltage drop on the span line will be large. In some instances, this would occur with an improper installation of equipment. In this situation, the voltage at the network element sink is lower. Since the network element sink will consume a fixed amount of power, it must consume more current to operate at a lower voltage. A critical point may be reached where the voltage drop on the span equals the input voltage at the network element sink, and is one half of the network element source output voltage and power. If the current increases beyond this point the network element sink power supply will drop out and cease to operate. At this point the power system will go through a re-boot process. As this is lengthy and will cause a service outage, this situation must be avoided.
Therefore, there is a need in the art for detecting line input voltage for line powered network elements and to provide an indicator.